The introduction of pourers or similar inserts by machine into the mouth of bottle-like containers is known; for instance, such pourers are disposed in a cap and, together with the cap, are applied to a container by a capping machine; or the pourers are introduced into the mouth of the container by an assembling tool. The pourer is intended to be wedged firmly in place in the mouth of the container as the result of elastic forces.
Problems frequently arise because of the fact that the bottle-like containers have particularly great tolerances. If the tolerance is positive, that is, if the inside diameter is larger than the intended dimension, then it is possible for the pourers to stick in the cap. If the tolerances are negative, that is, if the inner diameter of the mouth is smaller than the diameter of the insert, then substantial force must be exerted while introducing the insert into the mouth, with the attendant danger that the threads of the cap will be damaged.
There is also the further danger, in the case of positive tolerance, that when the contents are poured from the container the pourer may float out along with them. If this happens, it must be expected that the user will not reinsert the pourer, and then the required seal between the bottle-like container and the cap once the user has recapped the container will be lacking.
Bottles are also known whose mouth is larger at the top than at some lower point oriented toward the interior of the bottle. Here, again, it is difficult to anchor the pourer or insert in the mouth with sufficient holding power.